There's both maturity and comfort in Toni Braxton's voice. The 33-year-old Maryland native and multiplatinum R&B superstar has a rich, resonant alto etched with smoky shadings that belie her youthful appeal. That voice (along with some killer songs) helped make Braxton one of the most successful singers of the '90s. Beset with very public financial problems and contractual hassles, though, Braxton has been AWOL for four years. In that time a wave of younger (albeit less substantial) R&B performers has seized the spotlight. So it isn't surprising that Braxton's comeback single, "He Wasn't Man Enough," carries a sassy, hip-hop-flavored sound and a bitchy, biting attitude. As fun as the track is, Braxton's moody voice is better served by lush ballads and more dramatic midtempo songs. Unfortunately much of the material on The Heat never rises to the heights of previous hits like "Breathe Again" and "Love Shoulda Brought You Home." Indeed, the outstanding track here is the spare "The Art of Love." Sinewy and seductive, it is infused with the grown-up elegance and ease of Braxton at her best.